This invention relates to a method of controlling a sheet collator having a plurality of sheet loading pockets for receiving sheets to be collated. More particularly, this invention relates to a method of controlling sheet collators of the above mentioned type in a manner to detect missing or double sheet conditions and to allow appropriate intervention of the operator upon detection of missing or double sheet conditions. The invention further relates to a sheet collator suitable for performing the above method.
In a conventional sheet collator as disclosed in U.S. Pat. No. 3,887,176, a plurality of sheet loading pockets are arranged in parallel inclined relationship in a machine frame below a common sheet conveyor path. A sheet ejector is associated with each sheet loading pocket and adapted to eject single sheets from the associated sheet loading pocket into the generally horizontally extending common sheet conveyor path. Each sheet ejector comprises an ejection roller in frictional engagement with the uppermost sheet of the supply of sheets within the loading pocket. The drive of each sheet ejection roller is derived from the common driving motor of the collator also driving a plurality of opposed and engaging conveyor roller pairs arranged along the common sheet conveyor path. Each conveyor roller pair is mounted at the end of a deflection passage guiding each sheet ejected from the associated loading pocket into the nip formed between the two opposed rollers. In operation of the collator, each ejection roller is momentarily driven by actuation of a clutch arranged between each ejection roller and a common drive shaft. Each ejection roller is provided with a free wheeling system. When an ejected sheet is engaged in the entrance gap between two opposed conveyor rollers, the sheet will be completely moved out from its associated loading pocket although the ejection roller was only momentarily activated.
In a collating operation, care should be taken that each collated set of sheets is complete, i.e. that no sheets are missing. In order to check the completeness of each collated set, the conventional collator includes sheet passage detectors of contact switch type associated with each sheet ejector. Should any of the ejected sheet ejectors fail to supply a sheet towards the common sheet conveyor path, this would be detected by the associated sheet passage detector.
Sheet passage detectors of contact switch type are subject to wear and malfunctions after extended time of use. In addition, the activation of contact switches requires an activating force that can be afforded only by paper having considerable strength. Still further, while sheet passage detectors of contact switch type may be suitable to determine whether any sheet was ejected or not, they are unable to determine whether only a single or more than one sheet was ejected from the associated sheet pocket during a single ejection operation. Clearly, it is also desired to be able to check any collated set of sheets whether there are any sheets in excess of the total required number of sheets of a collated set, i.e. double or multiple sheets.